The present invention relates to an abrasive machine, more precisely relates to an abrasive machine capable of controlling a shape of an abrasive face of an abrasive plate so as to precisely abrade work pieces.
Abrasive machines have been widely used to abrade, polish or lap work pieces, e.g., semiconductor wafers, glass, crystals. A conventional abrasive machine is shown in FIG. 5. An abrasive plate 12 is held by a plate holder 14, and the holder plate 14 is provided on a base 50. The abrasive plate 12 is fixed to the plate holder 14 by bolts. The plate holder 14 is rotatably supported by a bearing 52, so that the plate holder 14 holding the abrasive plate 12 is capable of rotating with respect to the base 50. A rotary shaft 18 is fixed to the plate holder 14 and connected to a driving mechanism, e.g., a motor. The driving mechanism rotates the plate holder 14 together with the abrasive plate 12. An upper face (an abrasive face) of the abrasive plate 12 is covered with abrasive cloth 13 so as to polish work pieces.
A holding unit 30 holds and presses the work pieces, e.g., semiconductor wafers, onto the abrasive plate 12. The work pieces are sucked and held on a bottom face of a sucking board 32 of the holding unit 30. By rotating the holding unit 30 and the abrasive plate 12, the work pieces can be polished. Slurry is supplied to the abrasive cloth 13 from a nozzle 34.
Note that, a symbol 10 stands for an abrasive unit including the abrasive plate 12, the abrasive cloth 13 and the plate holder 14.
To make surfaces of the work pieces highly flat, flatness of the abrasive face of the abrasive plate 12 must be high. In some cases, the abrasive face of the abrasive plate 12 is slightly projected or depressed according to work pieces. To improve the flatness of the abrasive face of the abrasive plate, accuracy of machining the abrasive plate is made higher, thickness of the abrasive plate is made thicker, or the abrasive plate is made of a tough material. On the other hand, the abrasive face of the abrasive plate is projected or depressed by adjusting pressure of water for cooling the abrasive plate.
Frictional heat is generated between the abrasive face of the abrasive plate and the work pieces, so that the abrasive plate is expanded by the frictional heat. To prevent the heat expansion of the abrasive plate, the cooling water is introduced into water paths between the abrasive plate and the plate holder. For example, Japanese Patent Gazette No. 10-235552 disclosed a polishing machine in which an abrasive face of an abrasive plate is projected by adjusting pressure of cooling water running through water paths between the abrasive plate and a plate holder. Japanese Patent Gazette No. 11-307486 disclosed an abrasive machine in which a shape of an abrasive face is controlled projected by adjusting pressure of cooling water running through tubes between an abrasive plate and a plate holder.
FIG. 6 shows water paths 40 formed in an upper face of the plate holder 14. An inlet 45 of cooling water is formed at a center of the plate holder 14. The upper face of the plate holder 14 is divided into six sectors, and a zigzag water path 40 is formed in each of the sectors. An outlet 46 of the cooling water is formed in each of the sectors. The outlets 46 are located close to the inlet 45. The cooling water runs from the center to an outer edge part of the plate holder 14, then returns to the center thereof via the water paths 40. The cooling water returned to the center is discharged from the outlets 46.
FIG. 7 shows a sectional view of the abrasive unit 10. A water path 42 for supplying the cooling water and a water path 44 for discharging the cooling water are formed in the rotary shaft 18. The water paths 42 and 44 are connected to a water supply-discharge mechanism (not shown) via a distributor (not shown).
In FIG. 7, the water paths 40 are formed between the abrasive plate 12 and the plate holder 14.
In FIG. 7, the water paths 40 are formed between the abrasive plate 12 and the plate holder 14, so the shape of the abrasive face of the abrasive plate 12 can be controlled by controlling pressure of the cooling water running through the water paths 40. However, in the case of a small abrasive plate whose outer diameter is about 50 cm, the abrasive face is hardly deformed, so it is difficult to control the shape of the abrasive face by controlling the pressure of the cooling water. In the conventional abrasive unit 10 shown in FIG. 7, the abrasive plate 12 and the plate holder 14 are integrated other than the water paths 40, so it is difficult to deform the abrasive plate 12.
In the polishing machine disclosed in the Japanese Patent Gazette No. 10-235552, the cooling water runs between whole faces of the abrasive plate and the plate holder, but an outer edge of the abrasive plate is fixed to the plate holder. With this structure, the abrasive plate is hardly deformed.
The present invention is capable of solving the above described disadvantages of the conventional abrasive machines.
An object of the present invention is to provide an abrasive machine capable of controlling a shape of an abrasive face of a small abrasive plate so as to precisely abrade work pieces.
To achieve the object, the abrasive machine of the present invention comprises:
an abrasive plate;
a plate holder holding the abrasive plate;
a fixed engaging member being formed into a ring shape and fixed to the plate holder, the fixed engaging member engaging with an outer edge of the abrasive plate;
a first O-ring being provided between a pressing face of the fixed engaging member and an upper face of the abrasive plate, the first O-ring separating the pressing face of the fixed engaging member from the upper face of the abrasive plate;
a second O-ring being provided between an upper face of the plate holder and a lower face of the abrasive plate, the second O-ring separating the upper face of the plate holder from the lower face of the abrasive plate; and
a fluid supply-discharge mechanism for supplying a fluid to and discharging the same from a zone enclosed by the lower face of the abrasive plate, the upper face of the plate holder and the second O-ring, the fluid supply-discharge mechanism changing a shape of an abrasive face of the abrasive plate by changing pressure of the fluid,
wherein an outer circumferential face of the abrasive plate is separated from an inner circumferential face of the fixed engaging member.
In the abrasive machine of the present invention, the abrasive plate is held by the plate holder with the first and the second O-rings, which are respectively provided on the both sides of the abrasive plate. With this structure, the abrasive plate can be easily deformed, so that the shape of the abrasive face can be easily controlled by adjusting pressure of a fluid for cooling the abrasive plate. Further, the zone between the abrasive plate and the plate holder is tightly closed by the O-rings, so the fluid supplied by the fluid supply-discharge mechanism can be securely held in the zone.
In the abrasive machine, a position of the first O-ring in the upper face of the abrasive plate may correspond to that of the second O-ring in the lower face thereof. With this structure, the abrasive plate can be easily deformed, so that the shape of the abrasive face can be easily controlled.
In the abrasive machine, the fixed engaging member may include:
a fixed section being fixed to the plate holder; and
an extended section being inwardly extended from the inner circumferential face of the fixed engaging member and covering the outer edge of the abrasive plate.
In the abrasive machine, a step section may be formed in the outer edge of the abrasive plate, and the step section may be held by the extended section of the fixed engaging member.
In the abrasive machine, the abrasive plate may be made of a ceramic. By employing the ceramic abrasive plate, heat deformation of the abrasive plate can be prevented, and the shape of the abrasive face can be precisely controlled by adjusting pressure of a fluid for cooling the abrasive plate.